Install orginal HD with new ssd

Hello folks.. So I finally decided to purchase a new ssd (Samsung 850 EVO) I removed the old drive (WD 1 TB black) and put a fresh copy of windows on the SSD. Now heres the question If I want to reinstall my old drive to use as storage/backup how should I go about it? if it were a new hard drive it would be just a matter of plugging it in and do a format but this drive still has windows on it. so what's the best way to go about this ..thanks in advance

You can still connect it and format it like any drive, but make sure the BIOS is set to boot from the SSD first. You don't want to accidentally boot from the older drive, but you are fine to do what you want if you boot from the SSD. The Samsung and Western Digital drives should have different names in the BIOS, so checking and potentially changing their boot order should not be too difficult.

I've done this a few times before and actually keep the old drive with the Windows install still on it for a bit (and plugged in), in case I need to grab anything. (Actually I first clone the old drive to the new, so nothing should be needed, but I like to keep the backup for a bit, just in case something unexpected goes wrong.)